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Author Topic: How to precipitate ferric chloride?  (Read 5450 times)

Bill.D.Katt.

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How to precipitate ferric chloride?
« on: 22/03/2011 05:23:31 »
I have a solution of ferric chloride that is fairly concentrated, but contains a fair amount of HCl. FeCl2 is far more soluble in room temp solutions that in cold solutions so I dropped the temp to a little below 0 (C). I got a few crystals at the bottom, but after extracting them, drying them off, and placing them in a container, it turned back into a liquid. Any ideas why? Is the compound hygroscopic? Are there any other ways I can force the FeCl2 out of solution? I tried the common ion effect but for some reason it didn't work.

Bored chemist

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How to precipitate ferric chloride?
« Reply #1 on: 22/03/2011 06:51:53 »
Do you mean FeCl2 or FeCl3?

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How to precipitate ferric chloride?
« Reply #2 on: 22/03/2011 12:48:27 »
If it's ferric chloride, that is FeCl3 (not FeCl2) the eplanation is simple: the compound is highly hygroscopic and also partially hydrolizes in water forming HCl and brown ferric hydroxide (upon dilution).

Bill.D.Katt.

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How to precipitate ferric chloride?
« Reply #3 on: 23/03/2011 04:56:17 »
I think it is a mix of FeCl2 and FeCl3, considering the excess HCl I'm guessing it's predominantly FeCl3. So should I just wait until the water evaporates? I can't boil it right now (broken Pyrex beaker).

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How to precipitate ferric chloride?
« Reply #4 on: 23/03/2011 06:54:12 »
HCl will not turn FeCl3 into FeCl2.

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How to precipitate ferric chloride?
« Reply #5 on: 23/03/2011 10:42:58 »
If it's ferric chloride, that is FeCl3 (not FeCl2) the eplanation is simple: the compound is highly hygroscopic and also partially hydrolizes in water forming HCl and brown ferric hydroxide (upon dilution).
If you have also FeCl2 and you want FeCl3 only, you have to oxidize the solution: for example adding an excess of H2O2.

Bill.D.Katt.

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How to precipitate ferric chloride?
« Reply #6 on: 25/03/2011 04:32:27 »
I used a poor-mans aqua regia mix (HCl and 20% H2O2) to make the solution. I just said it was probably mostly FeCl3 because the electron config of Fe would seem a little more stable with all the s orbitals gone and a 1/2 d shell, twas just a guess. Anyway which one it is isn't the most trying part to me. I'm mostly trying to get it to precipitate out, and the methods I know for precipitation of solutes would be about the same for the two of them (however, both have failed). Although I noticed that when I added more H2O2 to the solution it bubbled quite vigorously; is this the H2O2 decomposing?

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How to precipitate ferric chloride?
« Reply #7 on: 25/03/2011 06:58:49 »
I think it would help if you started again.
What were you trying to achieve?
What did you do?
What did you observe?

Bill.D.Katt.

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How to precipitate ferric chloride?
« Reply #8 on: 26/03/2011 03:30:04 »
Here is the exact procedure that I did today: I have around 100 old BB's from which I have removed the Cu coating so only the steel is left. I add HCl (~34%, I'm guessing by volume) at this point the solution becomes significantly more yellow; wait an hour or so and add 20% H2O2 and the solution bubbles vigorously and becomes a deep murky brown (FeCl3 in solution?). This solution is highly acidic. I am attempting to force the FeCl3 from solution to obtain the (hexa)hydrated solid.

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How to precipitate ferric chloride?
« Reply #9 on: 26/03/2011 12:56:01 »
To make crystals of Fe3+ salts is extremely difficult, because of the hydrolysis:

Fe3+ + nH2O ↔ (FeOH)(2-n)+ + nH+, 1≤n≤3.

With FeCl3, when you try to dry it, even "naturally" at the air, you are left with a mix of FeCl3, Fe(OH)Cl2, Fe(OH)2Cl, Fe(OH)3 and HCl gone away with vapour.

Bill.D.Katt.

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How to precipitate ferric chloride?
« Reply #10 on: 26/03/2011 17:35:56 »
So how is it done? It looks like I need to maintain a high [H3O] while the solution is drying, is that right?

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How to precipitate ferric chloride?
« Reply #11 on: 26/03/2011 21:52:47 »
So how is it done?
Good question :)
Maybe they remove water vapour while keeping enough HCl vapour pressure in the container.

 

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